In a typical EL display device, a common electrode is located continuously throughout a plurality of pixels located on a substrate. An electrical voltage is applied to a portion of a light-emitting layer in each of the pixels, via the common electrode, from a periphery of the substrate. Consequently, due to electrical resistance of the common electrode, there is a tendency for electrical voltage applied to light-emitting layer portions in a central region of the substrate to be reduced relative to electrical voltage applied to light-emitting layer portions in a peripheral region of the substrate. As a consequence, uneven luminance of the light-emitting layer portions occurs between different pixels.
In one strategy for preventing a problem of voltage drop in the common electrode, electrical supply wiring is provided having stable conductivity across all of the light-emitting layer portions, and electrical power is supplied to the common electrode via the electrical supply wiring. The above configuration suppresses inequalities between the light-emitting layer portions in terms of applied electrical voltage.
FIG. 10 is a cross-sectional diagram illustrating a top-emission display device disclosed in Patent Literature 1 as one example of the EL display device including the electrical supply wiring. A display device 1000 includes a substrate 1001, a first electrode 1002 that functions as a pixel electrode, electrical supply wiring 1003, a hole injection layer 1004, a bank 1005, a light-emitting layer 1006, an electron transport layer 1007, and a second electrode 1008 that functions as a common electrode.
The first electrode 1002 and the electrical supply wiring 1003 are located on the substrate 1001 with an interval therebetween. The bank 1005 is located between the first electrode 1002 and the electrical supply wiring 1003.
The hole injection layer 1004, the light-emitting layer 1006, the electron transport layer 1007 and the second electrode 1008 are located above the first electrode 1002 in respective order. The display device 1000 is a top-emission display device. Therefore, the second electrode 1008 is for example made of a transparent conductive material such as indium tin oxide (ITO). ITO has a weak property of electron injection to the light-emitting layer 1006 compared to an alkali metal for example. Therefore, the electron transport layer 1007 is included between the second electrode 1008 and the light-emitting layer 1006. The electron transport layer 1007 is for example made of an organic material doped with alkali metal or alkaline earth metal (also referred to below as an organic electron transport layer). The property of electron injection can be improved through the doping with alkali metal or alkaline earth metal.
On the other hand, the second electrode 1008 is located above the electrical supply wiring 1003 with the electron transport layer 1007 therebetween. The electrical supply wiring 1003 is electrically connected to the second electrode 1008 through the above configuration.